The aim of this article is to draw attention to the special significance of docosahexaenoic acid (DHA) in the brain, the potential relevance of its abundance to the evolution of the brain in past history, and now the relevance of paucity in the food supply to the rise in mental ill-health.

Membrane lipids of photoreceptors, synapses, and neurons over the last 600 million years contained consistent and similarly high levels of DHA despite wide genomic change. The consistency is despite the DHA precursor differing only by 2 protons. This striking conservation is an example of Darwin's "Conditions of Existence," which he described as the higher force in evolution.

A purpose of this article is to suggest that the present paradigm of food production currently based on protein requirements, should change to serve the specific lipid needs of the brain to address the rise in mental ill-health.